Spring源码：声明式事务@Transactional源码分析--spring boot方式

目录

1. TransactionAutoConfiguration

2. @EnableTransactionManagement

3. TransactionManagementConfigurationSelector

3.1 AutoProxyRegistrar

3.2 ProxyTransactionManagementConfiguration

3.2.1 ProxyTransactionManagementConfiguration

3.2.2 AbstractTransactionManagementConfiguration

---

spring boot提供的一个很好的特性就是自动配置，能够省去很多手动配置带来的烦恼，大大提升项目的开发效率；这里spring对声明式事务的支持也从自动配置说起，spring对声明式事务的原生xml支持请移步：Spring源码：声明式事务@Transactional源码分析--spring xml实现

1. TransactionAutoConfiguration

/**
 * {@link org.springframework.boot.autoconfigure.EnableAutoConfiguration
 * Auto-configuration} for Spring transaction.
 *
 * @author Stephane Nicoll
 * @since 1.3.0
 */
@Configuration
@ConditionalOnClass(PlatformTransactionManager.class)
@AutoConfigureAfter({ JtaAutoConfiguration.class, HibernateJpaAutoConfiguration.class,
		DataSourceTransactionManagerAutoConfiguration.class,
		Neo4jDataAutoConfiguration.class })
@EnableConfigurationProperties(TransactionProperties.class)
public class TransactionAutoConfiguration {

	@Bean
	@ConditionalOnMissingBean
	public TransactionManagerCustomizers platformTransactionManagerCustomizers(
			ObjectProvider>> customizers) {
		return new TransactionManagerCustomizers(customizers.getIfAvailable());
	}

	@Configuration
	@ConditionalOnSingleCandidate(PlatformTransactionManager.class)
	public static class TransactionTemplateConfiguration {

		private final PlatformTransactionManager transactionManager;

		public TransactionTemplateConfiguration(
				PlatformTransactionManager transactionManager) {
			this.transactionManager = transactionManager;
		}

		@Bean
		@ConditionalOnMissingBean
		public TransactionTemplate transactionTemplate() {
			return new TransactionTemplate(this.transactionManager);
		}

	}

	@Configuration
	@ConditionalOnBean(PlatformTransactionManager.class)
	@ConditionalOnMissingBean(AbstractTransactionManagementConfiguration.class)
	public static class EnableTransactionManagementConfiguration {

		@Configuration
		@EnableTransactionManagement(proxyTargetClass = false)
		@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "false", matchIfMissing = false)
		public static class JdkDynamicAutoProxyConfiguration {

		}

		@Configuration
		@EnableTransactionManagement(proxyTargetClass = true)
		@ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "true", matchIfMissing = true)
		public static class CglibAutoProxyConfiguration {

		}

	}
}

由于在使用spring事务管理时，spring.aop.proxy-target-class默认为true，所以CglibAutoProxyConfiguration会生效，下面分析一下@EnableTransactionManagement的处理逻辑

2. @EnableTransactionManagement

EnableTransactionManagement主要定义了声明式事务代理目标类的方式、增强模式以及优先级，同时通过@Import注解导入了TransactionManagementConfigurationSelector implement ImportSelector，见如下源码，下面对TransactionManagementConfigurationSelector进行分析；

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {

	/**
	 * Indicate whether subclass-based (CGLIB) proxies are to be created ({@code true}) as
	 * opposed to standard Java interface-based proxies ({@code false}). The default is
	 * {@code false}. Applicable only if {@link #mode()} is set to
	 * {@link AdviceMode#PROXY}.
	 * 
Note that setting this attribute to {@code true} will affect all
	 * Spring-managed beans requiring proxying, not just those marked with
	 * {@code @Transactional}. For example, other beans marked with Spring's
	 * {@code @Async} annotation will be upgraded to subclass proxying at the same
	 * time. This approach has no negative impact in practice unless one is explicitly
	 * expecting one type of proxy vs another, e.g. in tests.
	 */
	boolean proxyTargetClass() default false;

	/**
	 * Indicate how transactional advice should be applied.
	 * 
The default is {@link AdviceMode#PROXY}.
	 * Please note that proxy mode allows for interception of calls through the proxy
	 * only. Local calls within the same class cannot get intercepted that way; an
	 * {@link Transactional} annotation on such a method within a local call will be
	 * ignored since Spring's interceptor does not even kick in for such a runtime
	 * scenario. For a more advanced mode of interception, consider switching this to
	 * {@link AdviceMode#ASPECTJ}.
	 */
	AdviceMode mode() default AdviceMode.PROXY;

	/**
	 * Indicate the ordering of the execution of the transaction advisor
	 * when multiple advices are applied at a specific joinpoint.
	 * 
The default is {@link Ordered#LOWEST_PRECEDENCE}.
	 */
	int order() default Ordered.LOWEST_PRECEDENCE;

}

3. TransactionManagementConfigurationSelector

其继承结构如下图：

可以看出TransactionManagementConfigurationSelector本质上是一个ImportSelector，具体导入了哪些类，通过如下代码可以看出，在采用AdviceMode.PROXY时，导入了AutoProxyRegistrar和ProxyTransactionManagementConfiguration，下面分别对这两个类进行分析；

/**
 * Selects which implementation of {@link AbstractTransactionManagementConfiguration}
 * should be used based on the value of {@link EnableTransactionManagement#mode} on the
 * importing {@code @Configuration} class.
 *
 * @author Chris Beams
 * @since 3.1
 * @see EnableTransactionManagement
 * @see ProxyTransactionManagementConfiguration
 * @see TransactionManagementConfigUtils#TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME
 */
public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector {

	/**
	 * {@inheritDoc}
	 * @return {@link ProxyTransactionManagementConfiguration} or
	 * {@code AspectJTransactionManagementConfiguration} for {@code PROXY} and
	 * {@code ASPECTJ} values of {@link EnableTransactionManagement#mode()}, respectively
	 */
	@Override
	protected String[] selectImports(AdviceMode adviceMode) {
		switch (adviceMode) {
			case PROXY:
				return new String[] {AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};
			case ASPECTJ:
				return new String[] {TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME};
			default:
				return null;
		}
	}

}

3.1 AutoProxyRegistrar

AutoProxyRegistrar的具体实现如下，通过AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry)的方式注册了beandefinition：InfrastructureAdvisorAutoProxyCreator，和spring xml声明式事务导入了同样的自动代理创建类，完成代理的创建过程；

/**
 * Registers an auto proxy creator against the current {@link BeanDefinitionRegistry}
 * as appropriate based on an {@code @Enable*} annotation having {@code mode} and
 * {@code proxyTargetClass} attributes set to the correct values.
 *
 * @author Chris Beams
 * @since 3.1
 * @see EnableAspectJAutoProxy
 */
public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {

	private final Log logger = LogFactory.getLog(getClass());

	/**
	 * Register, escalate, and configure the standard auto proxy creator (APC) against the
	 * given registry. Works by finding the nearest annotation declared on the importing
	 * {@code @Configuration} class that has both {@code mode} and {@code proxyTargetClass}
	 * attributes. If {@code mode} is set to {@code PROXY}, the APC is registered; if
	 * {@code proxyTargetClass} is set to {@code true}, then the APC is forced to use
	 * subclass (CGLIB) proxying.
	 * 
Several {@code @Enable*} annotations expose both {@code mode} and
	 * {@code proxyTargetClass} attributes. It is important to note that most of these
	 * capabilities end up sharing a {@linkplain AopConfigUtils#AUTO_PROXY_CREATOR_BEAN_NAME
	 * single APC}. For this reason, this implementation doesn't "care" exactly which
	 * annotation it finds -- as long as it exposes the right {@code mode} and
	 * {@code proxyTargetClass} attributes, the APC can be registered and configured all
	 * the same.
	 */
	@Override
	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
		boolean candidateFound = false;
		Set annoTypes = importingClassMetadata.getAnnotationTypes();
		for (String annoType : annoTypes) {
			AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annoType);
			if (candidate == null) {
				continue;
			}
			Object mode = candidate.get("mode");
			Object proxyTargetClass = candidate.get("proxyTargetClass");
			if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&
					Boolean.class == proxyTargetClass.getClass()) {
				candidateFound = true;
				if (mode == AdviceMode.PROXY) {
					AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
					if ((Boolean) proxyTargetClass) {
						AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
						return;
					}
				}
			}
		}
		if (!candidateFound) {
			String name = getClass().getSimpleName();
			logger.warn(String.format("%s was imported but no annotations were found " +
					"having both 'mode' and 'proxyTargetClass' attributes of type " +
					"AdviceMode and boolean respectively. This means that auto proxy " +
					"creator registration and configuration may not have occurred as " +
					"intended, and components may not be proxied as expected. Check to " +
					"ensure that %s has been @Import'ed on the same class where these " +
					"annotations are declared; otherwise remove the import of %s " +
					"altogether.", name, name, name));
		}
	}
}

3.2 ProxyTransactionManagementConfiguration

继承结构如下：

下面分别对ProxyTransactionManagementConfiguration和AbstractTransactionManagementConfiguration进行说明；

3.2.1 ProxyTransactionManagementConfiguration

源码如下，可见该类是一个Configuration类，完成了如下3个bean的定义：

• AnnotationTransactionAttributeSource
• TransactionInterceptor
• BeanFactoryTransactionAttributeSourceAdvisor

这和spring xml声明式事务的定义完全一致；

/**
 * {@code @Configuration} class that registers the Spring infrastructure beans
 * necessary to enable proxy-based annotation-driven transaction management.
 *
 * @author Chris Beams
 * @since 3.1
 * @see EnableTransactionManagement
 * @see TransactionManagementConfigurationSelector
 */
@Configuration
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {

	@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {
		BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
		advisor.setTransactionAttributeSource(transactionAttributeSource());
		advisor.setAdvice(transactionInterceptor());
		advisor.setOrder(this.enableTx.getNumber("order"));
		return advisor;
	}

	@Bean
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public TransactionAttributeSource transactionAttributeSource() {
		return new AnnotationTransactionAttributeSource();
	}

	@Bean
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public TransactionInterceptor transactionInterceptor() {
		TransactionInterceptor interceptor = new TransactionInterceptor();
		interceptor.setTransactionAttributeSource(transactionAttributeSource());
		if (this.txManager != null) {
			interceptor.setTransactionManager(this.txManager);
		}
		return interceptor;
	}
}

3.2.2 AbstractTransactionManagementConfiguration

AbstractTransactionManagementConfiguration主要完成了@EnableTransactionManagement注解属性的解析，同时通过注入TransactionManagementConfigurer类型的bean，完成事务管理器PlatformTransactionManager的设置，如下：

/**
 * Abstract base {@code @Configuration} class providing common structure for enabling
 * Spring's annotation-driven transaction management capability.
 *
 * @author Chris Beams
 * @author Stephane Nicoll
 * @since 3.1
 * @see EnableTransactionManagement
 */
@Configuration
public abstract class AbstractTransactionManagementConfiguration implements ImportAware {

	protected AnnotationAttributes enableTx;

	/**
	 * Default transaction manager, as configured through a {@link TransactionManagementConfigurer}.
	 */
	protected PlatformTransactionManager txManager;


	@Override
	public void setImportMetadata(AnnotationMetadata importMetadata) {
		this.enableTx = AnnotationAttributes.fromMap(
				importMetadata.getAnnotationAttributes(EnableTransactionManagement.class.getName(), false));
		if (this.enableTx == null) {
			throw new IllegalArgumentException(
					"@EnableTransactionManagement is not present on importing class " + importMetadata.getClassName());
		}
	}

	@Autowired(required = false)
	void setConfigurers(Collection configurers) {
		if (CollectionUtils.isEmpty(configurers)) {
			return;
		}
		if (configurers.size() > 1) {
			throw new IllegalStateException("Only one TransactionManagementConfigurer may exist");
		}
		TransactionManagementConfigurer configurer = configurers.iterator().next();
		this.txManager = configurer.annotationDrivenTransactionManager();
	}


	@Bean(name = TransactionManagementConfigUtils.TRANSACTIONAL_EVENT_LISTENER_FACTORY_BEAN_NAME)
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public TransactionalEventListenerFactory transactionalEventListenerFactory() {
		return new TransactionalEventListenerFactory();
	}

}

综上，spring声明式事务xml配置形式和spring boot自动配置形式完全一致，均完成了对spring声明式事务的支持；